1. Field of the Invention
The invention relates to ignition systems for multi-cylindered, internal combustion engines and, in particular, to means for retrofitting a breaker-type ignition system to a breakerless system without replacement of the breaker cam and its associated mechanical linkage to the centrifugal advance mechanism customarily present in automotive distributors.
2. Description of the Prior Art
The breaker point system which has been commonly employed in the Kettering ignition systems of internal combustion engines has many serious operating defects. Since the breaker points are mechanically actuated, they can lose precise adjustment, i.e., become untuned, from wear and vibration. The points or contacts also wear and pit from electrical discharges as they are opened and closed. The opening and closing cycle also requires a finite period of time and systems for use with high speed engines have required the use of multiple sets of points and other encumbrances.
The increasing concern over environmental quality has aggravated the problems of the breaker point system. Minimum emissions of noxious gases such as nitrogen oxides, imcomplete combustion products, etc., can only be achieved when the ignition system is in precise adjustment. The degree of maladjustment of the breaker points in an ignition system which has, heretofore, been commonly tolerated is not acceptable when close control over emissions is desired. Additionally, energy is wasted by untuned engines. Frequent replacement of the breaker points and tuning of engines or the development of a substitute, breakerless ignition system is, therefore, required.
Various breakerless distributors and electronic ignition systems have been proposed and such systems are presently available as standard or optional equipment in the present new cars. The breakerless ignition systems which are available as original equipment, however, are not readily compatible with prior ignition systems and conversion of the ignition system of an older vehicle with such systems requires replacement of a number of expensive components of the ignition system.
Some attempts have been made to provide kits that can be used to retrofit breaker-type ignition systems to breakerless systems. These attempts have either employed the breaker cam of the existing ignition system directly as a magnetic pulse wheel, as in U.S. Pat. No. 3,291,108, and U.S. Pat. No. 3,328,614. These attempts have not been successful because the shape of a breaker cam prohibits the induction of a voltage pulse of sufficient magnitude in the pick-up coil of the ignition system, particularly at low engine speeds, to permit design of an entirely reliable ignition circuit.
Other investigators have suggested mounting pulse wheels or magnetic flux wheels onto the breaker cam of an ignition system to retrofit the latter to a breakerless system. Of these, U.S. Pat. No. 3,272,930 suggests that a spider of ferromagnetic segments be mounted onto a magnetically insulating sleeve or body and that the latter be placed over the breaker cam. This attempt could never provide a reliable ignition system and the failings of the aforedescribed patent are recognized in U.S. Pat. No. 3,249,707, which describes a magnetic pulse wheel that is formed from a plurality of laminations of alternating layers of a magnetically permeable metal and of a resilient metal for gripping onto the exterior surfaces of the distributor cam. The approach of this patent adds to the complexity of the retrofitting task and compromises the magnetic flux permeability of the pulse wheel by inadequate metal-to-metal contacting with the cam surfaces.